In detonating blasting charges, transmission tubes are frequently used, being deployed from a central initiating point to send a signal to detonate individual blasting charges.
The transmission tube may be of the type disclosed in U.S. Pat. No. 3,590,739, sold under the trademark "NONEL", and sometimes referred to as "shock tube". As used herein, the term "transmission tube" refers to any detonating or deflagrating signal transmission tube or line including flexible hollow tube, which can carry a detonating signal or deflagrating signal along its interior, which signal may not destroy the tube.
The term "signal" when used in connection with the aforementioned transmission tube is intended to refer to both the detonating shock wave or deflagrating flame front which is transmitted along the (interior of the) tube by combustion of the reactive substances contained therein. A detonator may be activated by first initiating a transmission tube, which transmits a signal by propagating a temperature/pressure reaction down its length and to the detonator. The incoming signal ignites a reactive pyrotechnic composition in the detonator, which in turn ignites an explosive output charge.
There are a number of prior art methods of initiating a signal in a transmission tube using percussion initiated or electrically initiated charges. However, these prior art initiation methods require that the transmission tube environmental seal be broken before initiation to expose the tube reactive substance to the initiating charge. The exposed reactive substance must be aligned with the charge so that when the charge is functioned the reactive substance is ignited thereby initiating signal propagation in the tube.
There are a number of problems associated with these prior art initiation devices. A first problem is that the alignment of certain of the tube reactive substances with the initiation charge may be required to be precise for reliable initiation. Another problem is the fact that the tube reactive substance may be exposed to moisture and other potential environmental contaminants at the location of the proposed point of tube initiation, i.e., at the point of breakage in the tube environment seal, which in turn could cause desensitization of the reactive material and prevent reliable initiation of a signal in the transmission tube. This is of particular concern when tube initiation is desired in rainy weather or wet environments. Yet another problem is that the Department of Transportation regulates the transportation of explosives and explosive initiation devices because of their highly reactive nature, thereby resulting in high transportation costs.
It is therefore a primary object of the invention to provide an improved signal initiation device for reliable non-intrusive initiation of a transmission tube;
it is another object of the invention to provide a signal initiation device which is particularly well suited for reliable signal initiation of a transmission tube in a variety of wet environments;
it is a further object of the invention to provide a signal initiation device which may be stored and transported in an inherently safe condition, and therefor, at a reduced cost without restrictive regulations;
it is another object of the invention to provide a signal initiation device which is adaptable to be used with a variety of known firing devices; and
it is a further object of the invention to provide a signal initiation device for reliable initiation of a transmission tube while maintaining the integrity of the transmission tube and thereby preventing environmental contamination of the transmission tube reactive material.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.
A better understanding of the objects, advantages, features, properties and relations of the invention will be obtained from the following description and accompanying drawings which set forth certain illustrative embodiments and are indicative of the various ways in which the principles of the invention are employed.